This invention relates to an air circuit interrupter and more particularly to an air circuit interrupter in which, after the energy storing spring is charged by the operation of the circuit interrupter handle, the current carrying portion is closed and opened at command by the charged spring force. Generally, this kind of circuit interrupter is used for a main electrical circuit for low voltage distribution and, perferably, has a large interrupting capacity and is as compact as possible.
FIGS. 1 to 3 show a conventional air circuit interrupter as disclosed in Japanese Patent Laid Open No. 58-129720 for example, in which 1 is an operating handle pivotably supported by a shaft 2, 3 is a first cam driven by the operating handle 1 for rotation, 4 is a charge lever engaging with the operating lever 1 and driven to rotate, 5 is an energy storing spring chargeable by the charge lever 4, 6 is a link mechanism for transmitting the spring force of the energy storing spring 5 to a contact operating mechanism side and is comprised of a pair of links 6a and 6b or the like. A direction changing lever 7 is pivotably supported by a pivot shaft 7a, its lower end portion being connected to the link 6a and the upper end portion being connected to an insulating link 8 which constitutes a part of the contact operating mechanism which will be described later. A pair of conductors 9a and 9b constitute a part of the current carrying portion, 10 is a main stationary contact secured to the conductor 9a, 11 is a main movable contact engaging and separating relative to the stationary contact 10, 12 is a movable member on which the movable contact 11 is secured, 13 is a movable member holder for holding the movable member 12 having connected to its upper end portion the insulating link 8. A contacting pressure spring 14 biases the movable member 12 in the direction of contact closing, this contacting spring 14 constituting, together with the movable member 12, the holder 13 and the insulating link 8, the contact operating mechanism. A throw-in latch 15 is rotatably supported by a pivot shaft 16, which is rotated counterclockwise by a D-shaped latch 17 on an ON operating member side which releases the contact closing waiting state. A trip latch 18 is pivotally supported by the pivot shaft 16 and biased in the counterclockwise direction by the return spring 19, 20 is a second cam rotatably supported by a shaft 21 and biased counterclockwise by a return spring 22, which has a recessed portion 20a for engaging the engaging roller 18a on the lower end portion of the trip latch 18, so that the clockwise compressive force is applied against the trip latch 18 against the spring force of the return spring. A strut link 23 is connected between a pin 20b of the second cam 20 and the pin 6c of the link mechanism 6, 24 is a D-shaped latch which is engageable with the engaging portion 18b of the trip latch 18 to prevent the clockwise rotation of the trip latch 18 and which constitutes, together with the trip latch 18 and the second cam 20, a contact-opening-waiting mechanism This mechanism maintains the link mechanism 6 extended against the spring force of the contacting pressure spring 14 and the electromagnetic repulsive force acting on the current carrying member due to a current above a predetermined value. The D-shaped latch 24 is rotated clockwise by the OFF operating member (not shown) for releasing the contact-opening-waiting state.
The operation will next be explained. In the state shown in FIGS. 1 and 2, the direction changing lever 7 is biased and rotated counterclockwise by the spring force of the contacting pressure spring 14 causing the spring to extend, and the link mechanism 6 is subjected to a force which causes the mechanism 6 to be folded at the pin 6c in the direction of an arrow 25. However, since the second cam 20 is blocked by the trip latch 18 and is not rotated clockwise, the mechanism 6 is maintained in the illustrated state. This state is referred to as the contact-opening-waiting state. In this state, the clockwise rotational force on the second cam 20 driven by the strut link 23 against the return spring 22 is blocked by the trip latch 18 engaging the engaging portion 18b at the D-shaped latch 24.
As shown in FIG. 3, when the D-shaped latch 24 is rotated clockwise by the operation of the OFF operating member, since the trip latch 18 is slightly rotated clockwise against the spring force of the return spring 19, the recessed portion 20a disengages from the engaging roller 18a and the second cam 20 is rotated clockwise by the action of the contacting pressure spring 14 shown by the arrow 25 of FIG. 2. Therefore, the strut function of the link 23 is lost and the link mechanism 6 is collapsed. This movement causes the separation of the contacts 10 and 11 as shown in FIG. 3. The explanation of the operation for charging the energy storing spring 5 and the ON operation is omitted.
In this air circuit interrupter, an abnormal current in the circuit is quickly interrupted by manually rotating the D-shaped latch 24 for opening the OFF operating member side in the clockwise direction, or by detecting an abnormal current flowing in the interrupter by a current transformer (not shown) or the like to excite the electromagnetic coil (not shown) in accordance with the inverse time delay characteristics by the electric control unit of the trip relay (not shown). The rated interrupting current of the interrupter at this time means maximum current which is in accordance with the inverse time delay characteristics and which is capable of being interrupted by that interrupter without causing thermal or electromagnetic damages within the interrupting time period.
Also, in this air circuit interrupter, since the interrupting capacity is determined by designing the link mechanism 6 or the like in accordance with the rated interrupting current, the higher the rated interrupting current the bigger the dimensions of the link mechanism 6 or the like, resulting in a large frame size of the interrupter, and also with the same rated interrupting current and the frame size, the higher the interrupting capacity the shorter the interrupting time period.
The interrupting time is the time period composed of the relay time during which the current is detected and the opening D-shaped latch 24 is rotated by an electromagnetic coil or the like, the opening time from the rotation of the D-shaped latch 24 for collapsing the link mechanism 6 to the initiation of the separation of the contacts 10 and 11, and the arcing time during which the arc is generated between the contacts 10 and 11 and is extinguished.
In the above-described conventional air circuit interrupter, since the interrupting time is substantially constant, the problem arises that as the interrupting capacity increases the rated interrupting current as well as the frame size increase.